Exposure to Cholera Toxin, can result in diarrhoea resulting in severe dehydration due to excessive water loss. Why might this be detrimental to neuronal homeostasis and what is the consequence?

Question

BlackTom AI · Accepted Answer

Loss of extracellular water concentrates ions; a rise in extracellular K+ ([K+]o) is particularly disruptive to neuronal membrane potentials. Key points: resting membrane potential is largely set by the K+ gradient (inside ~140 mM, outside ~3–4 mM) and the Nernst potential for K+. During an action potential, voltage-gated K+ channels open and K+ efflux repolarises the membrane; the driving force for that efflux depends on the electrochemical gradient for K+.

Step-by-step reasoning:
1. Use the Nernst equation for K+ at physiological temperature (approximate form): E_K ≈ -61.5 log([K+]i/[K+]o).
2. Baseline example: [K+]i = 140 mM, [K+]o = 4 mM → log(140/4) = log(35) ≈ 1.544 → E_K ≈ -61.5 × 1.544 ≈ -95 mV.
3. If dehydration raises [K+]o to 8 mM (example doubling): log(140/8) = log(17.5) ≈ 1.243 → E_K ≈ -61.5 × 1.243 ≈ -76.5 mV.
4. E_K becomes ~19 mV less negative, so the driving force for K+ efflux during repolarisation is reduced. With less K+ leaving, repolarisation is slowed and the membrane potential is less negative (depolarised). This impairs the normal return to resting potential after depolarisation and can disrupt neuronal signaling.

Why the correct option is correct: it explicitly states increased extracellular K+ reduces the K+ electrochemical gradient and decreases repolarisation — matching the Nernst-based reasoning and physiological role of K+ in repolarisation.

Why other options are incorrect:
- Options invoking increased extracellular Na+ focus on increasing Na+ gradient/excitability. Moderate changes in [Na+]o have less effect on AP amplitude (Na+ reversal potential ~+60 mV) and neuronal excitability is primarily determined by K+-mediated resting potential; dehydration’s most critical effect is on K+ handling.
- The last option correctly identifies decreased K+ gradient but wrongly claims increased K+ conductance; elevated [K+]o does not intrinsically increase K+ conductance and severe hyperkalaemia can inactivate Na+ channels, reducing excitability.

Conclusion: The correct answer is: "Increases extracellular K+ ion concentration → decreasing the electrochemical gradient for K+ → decrease repolarisation of membrane potential following depolarisation." This matches the provided answer.

Exposure to Cholera Toxin, can result in diarrhoea resulting in severe dehydration due to excessive water loss. Why might this be detrimental to neuronal homeostasis and what is the consequence?单项选择题

类似问题

Neuron X is at its resting membrane potential of -65 mV, with standard resting membrane permeabilities, and standard intracellular and extracellular concentrations of sodium, potassium, chloride and calcium. In which direction will K+ move across the membrane when its selective channel opens?

In a neuron with a resting membrane potential of -65mV, the distribution of which ion across the neuronal membrane represents the greatest electrical potential?

In a two-compartment model of a cell with a K +- and Cl --permeable membrane and a 10-fold excess of K + in the inside compartment, how would the membrane potential change if all K + ions were replaced by Cl - ions?

Which statement regarding membrane potential and equilibrium potential is true?

A group of neurons expresses a pump which actively transports Vz2- into the cell, and also expresses a limited number of Vz2- leak channels in the cell membrane. Which voltage would most closely represent EVz in these neurons?

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单